UML and Patterns - Absolute Java - page 695

Self-Test Exercises (continued)

3. Suppose aStudent is an object of the class Student . Based on the inheritance
diagram in Display 12.3, where will you find the definition of the method used
in the following invocation? Explain your answer.

aStudent.setNumber(4242);

12.2 Patterns ★

I bid him look into the lives of men as though into a mirror, and from others to
take an example for himself.

TERENCE (Publius Terentius Afer) 190-159 B.C., Adelphoe

pattern Patterns are design outlines that apply across a variety of software applications. To

be useful, the pattern must apply across a variety of situations. To be substantive,
the pattern must make some assumptions about the domain of applications to which
it applies. For example, one well-known pattern is the Container-Iterator pattern.
A container is a class (or other construct) whose objects hold multiple pieces of data.
One example of a container is an array. Other examples, which will be discussed later
in this topic, are vectors and linked lists. Any class or other construct designed to
hold multiple values can be viewed as a container. For example, a String value can
be viewed as a container that contains the characters in the string. Any construct that
allows you to cycle through all the items in a container is an iterator . For example, an
array index is an iterator for an array. It can cycle through the array as follows:

Container-
Iterator

container

iterator

for ( int i; i < a.length; i++)
Do something with a[i]
The index variable i is the iterator. The Container-Iterator pattern describes how an
iterator is used on a container.
In this brief chapter, we can give you only a taste of what patterns are all about. In
this section, we will discuss a few sample patterns to let you see what patterns look like.
There are many more known and used patterns and many more yet to be explicated.
This is a new and still developing field of software engineering.

Adaptor Pattern ★
The Adaptor or Adapter pattern transforms one class into a different class without
changing the underlying class but merely by adding a new interface. (The new interface
replaces the old interface of the underlying class.) For example, in Chapter 11, we
mentioned the stack data structure, which is used to, among other things, keep track
of recursion. One way to create a stack data structure is to start with an array and add

Adaptor